3,9-Bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (hereinafter also referred to as “spiroglycol”) is used mainly as a resin raw material. A spiroglycol is conventionally synthesized by subjecting hydroxypivalaldehyde (hereinafter also referred to as “HPA”) and pentaerythritol (hereinafter also referred to as “PE”) to an acetalization reaction under an acid catalyst in an aqueous solution. Then, after neutralizing the resultant reaction solution with an alkali, crystals of the spiroglycol precipitated during the reaction are filtered, washed with water and dried to obtain a product.
As a production method for such a spiroglycol, for example, a method in which HPA is reacted with PE in a water solvent using an acid catalyst to obtain a reaction product solution, the reaction product solution is neutralized with an alkali, and the neutralized reaction product solution is heated to 75 to 100° C. to produce a spiroglycol (see, for example, Patent Literature 1); a method in which HPA is reacted with PE in a water solvent using an acid catalyst to obtain a reaction product solution, the reaction product solution is adjusted to pH 7 or more with an alkali to obtain a slurry mixture, and the thus obtained slurry mixture is subjected to a heat treatment at 120° C. or more to produce a spiroglycol (see, for example, Patent Literature 2); and a method in which HPA is reacted with PE using an acid catalyst in a mixed solvent containing an organic solvent immiscible with water and water to produce a spiroglycol (see, for example, Patent Literature 3), which have been proposed. It is noted that HPA used as a raw material is conventionally obtained through an aldol condensation reaction of isobutyraldehyde and formaldehyde performed in the presence of a basic catalyst.
Besides, as a method for industrially advantageously producing a spiroglycol having a sufficiently high purity, a production method for a spiroglycol has been known, where PE is reacted with HPA using an acid catalyst to obtain a reaction solution (slurry) containing a prescribed amount of a spiroglycol, the reaction solution is filtered without neutralization to separate the spiroglycol, and a part of the thus obtained filtrate is reused in the reaction of the next cycle has been known (see, for example, Patent Literature 4). Furthermore, as a method for producing a spiroglycol having a sufficient purity, a method has been known, where a crude spiroglycol obtained through a reaction of PE and HPA is dissolved in an organic solvent, water is added to the thus obtained solution for extracting and removing an impurity into water, an aqueous layer and an organic layer are separated, and the organic layer is cooled to recrystallize a spiroglycol (see, for example, Patent Literature 5). In addition, as a method for producing a spiroglycol having a sufficiently high purity, a production method for a spiroglycol including a step of bringing hydroxypivalaldehyde used as a raw material of a spiroglycol into contact with an oxygen-containing gas in advance has been known (see, for example, Patent Literature 6).